Wynonna Says Kirstie Alley Is Her Dancing with the Stars Weight Loss 'Mentor'

Despite playfully telling Tuesday's Good Morning America audience about signing on to Dancing with the Stars so that she can get down to her birth weight, the singer says her health has actually become a growing concern.

"This is a great diversion for me, because it will focus on self-care, which for women – especially working as hard as I do – we forget to put ourselves on the list," Wynonna, 48, told PEOPLE shortly after it was announced she'd be joining the cast of ABC's hit show. "This will force me to take care of myself."

"I definitely went into being the wife and caretaker, and I let myself go in terms of way down the list," she says. "There were days and days and days that I didn't walk. I'm a walker, and I'm always telling my fans how to be healthy. It's not about size and numbers, but I can honestly say I've seen the pictures from when I got married and before, and I see them now and I think, 'You know what? I deserve to be healthy. I'm worth it.' "

Wynonna calls her pal and two-time former Dancing contestant, Kirstie Alley, 62, her "mentor in this process."

Says the singer, "I've talked to Kirstie so many times. She said if you have fun and you do everything that you're going to be doing with your heart, the rest will follow. I really believe that. She really misses [the show]."

Wynonna, who is partnered with last season's all-star winner, Tony Dovolani, is eager to surprise viewers.

"It's cool because I don't think a lot of people thought that I would be doing this show," she says. "There's a little bit of me that goes, 'Oh, really? Watch this.' I do have a competitive part of me."